1. Technical Field
The present invention relates to an image processing device, an image processing method, and an image processing program, which process an frame image of an imaging area imaged with an infrared camera and generates a background difference image.
2. Related Art
Conventionally, a monitoring system that monitors an invasion of a suspicious person or a left suspicious object using imaging devices, such as a video camera, is in practical use. In this kind of monitoring system, an imaging area of the imaging device is adjusted to a monitoring target area where the invasion of the suspicious person or the left suspicious object is monitored. The monitoring system also includes an image processing device that processes the frame image of the monitoring target area imaged with the imaging device and detects imaged objects, such as the suspicious person and the suspicious object.
Using a background model, the image processing device determines whether each pixel of the input frame image is a background pixel in which a background is imaged or a foreground pixel in which the object except the background is imaged. Based on a determination result, the image processing device generates a background difference image (a binary image) in which a background region where the background is imaged and a foreground region where objects, such as a person and a vehicle, are imaged are separated from each other. The foreground region of the background difference image is the region where the object is imaged.
On the other hand, a visible light camera cannot image the object that is of a detection target in a relatively dark place because of an insufficient exposure amount. Therefore, for example, Japanese Unexamined Patent Publication No. 2006-101384 proposes a device that processes the frame image (a thermal image) taken with a far-infrared camera and detects the imaged person.
In a configuration of the device disclosed in Japanese Unexamined Patent Publication No. 2006-101384, a binary image is generated by dividing each pixel of the thermal image taken by the far-infrared camera into a pixel located within a range between an upper limit threshold and a lower limit threshold of a luminance value (a pixel value) corresponding to a temperature of a person and a pixel located outside the range, and the imaged person is detected.
However, contrasts of objects, such as the person and the vehicle, which are imaged in the frame image taken with the far-infrared camera are degraded because the person and the vehicle that are of the detection target objects is rainy in the rainfall time. Therefore, even if objects, such as the person and the vehicle, which are imaged in the frame image taken with the far-infrared camera can be detected in fine weather or cloudiness, sometimes the objects cannot be detected in the rainfall time.
Sometimes a change in weather of the imaging area of the far-infrared camera degrades detection accuracy of objects, such as the person and the vehicle, which are imaged in the frame image taken with the far-infrared camera.